Diastereoselective Formation of Complexed Methylenediphosphiranes

Stable syn-substituted methylenediphosphirane complexes are obtained from the reaction of transient, electrophilic phosphinidenes [R−PW(CO)5] (R = Me, Ph), thermally generated from the corresponding benzophosphepines, with 1-phosphaallene. A DFT analysis at the B3PW91/6-31G(d) level of theory reveals that the high diastereoselectivity of this reaction results from the preferred negative activation energy for syn cyclization of the P,P-ylide intermediates.